1) Field
The invention concerns mobile communication networks offering circuit-switched (CS) connectivity and Internet Protocol (IP) connectivity, and more precisely concerns controlling the access of subscriber terminals of the CS domain of a mobile communication network to services of an IMS (IP Multimedia (core network) Subsystem) communication network.
2) Related Art
As the person skilled in the art is aware, the operators of certain communication networks offering IP connectivity, for example the GPRS and UMTS networks, have developed IMS domains that offer specific services to customers who register with them (or subscribe to these services). For example, using the Session Initiation Protocol (SIP), it is possible to display on the screen of a communication terminal connected to an IMS domain a personal Internet page of the caller, or to make available enhanced voice communication services or IP multimedia services or instant messaging services, or to cause different terminals belonging to the same user to ring when he is called.
At the access network level, the IMS domain is based on a packet-switched (PS) access domain, for example a GPRS network, or a domain of a fixed communication network, for example an ADSL network, or a domain of a wireless local area network (WLAN).
In order to enable customers of CS domains to set up calls with customers of IMS domains, the core networks of the above networks include functional modules called media gateway control function (MGCF) modules and associated media gateways. The latter are responsible for converting signaling protocols used by the CS domains, for example ISUP or BICC, into IMS signaling protocols, for example SIP, and vice-versa. They therefore provide the interconnection between the IMS networks and the switched telephone networks, such as PSTN, ISDN, and the CS domains of mobile networks (PLMN).
Thanks to these MGCF modules (and the associated media gateways) a mobile telephone connected to a CS domain of a mobile network (PLMN) can set up a voice call with any mobile telephone connected to any IMS domain of any operator, for example. However, it cannot obtain the benefit of services offered by those IMS domains.